One way to express global costs is as a percentage of the present costs of protection and maintenance. The first attempt of this kind was undertaken by Vellinga52 at a meeting of the UNEPWMO-ICSU Advisory Group on Greenhouse Gases held in Villach, Austria. Figure 5 shows the results of this assessment.

Four scenarios are assumed. The lower bound estimate assumes that all the nations of the world join in a strenuous effort to limit the greenhouse effect and to implement immediately appropriate defences against rising sea levels. By contrast, the upper bound assumes that no attempts are made at limitation or adaptation, thus resulting in astronomical costs within 40-50 years. The intermediate scenarios assume either that unlimited emissions of greenhouse gases are accompanied by a positive adaptation programme or that greenhouse gases are limited to some extent and that only minimal adaptation is attempted. It seems most likely that some countries will emphasize limitation and others adaptation, and that the world at large will do a little of both, but not as much as might be necessary.

Figure 5 is based on two assumptions: (1) that the future costs of climatic change, and sea level rise in particular, are already clear enough to justify action; and (2) that the measures needed to abate or adapt to climatic change and rising sea levels must be accomplished within the next 3-4 decades i f they are to be effective in time. The results imply that, regardless of the scenario chosen, the relative costs and impacts will be about the same until 2025-2030, but will diverge widely thereafter. However, the lack of divergence until 2025-2030 should not be taken as an argument for postponing decisions until then. The critical period for response will still be in the order of 3-4 decades.

10

Recommended Action

The Advisory Group on Greenhouse Gases has proposed that a number of actions be taken in response to the threat of climatic change. Of these, the most important are:

•Immediate steps to limit greenhouse gases in the atmosphere. This would involve:

More detailed recommendations have been made by the World Resources Institute, which suggests various strategies for controlling emissions of C02, CH4, N20 and CFCs. Several others have also presented proposals similar to those of the WRI.53

Yet, even with the best technological innovations and with societal adaptations, there will be a slow build-up of greenhouse warming by 2075 of between 1°C-3°C. With only modest policies (involving the use of best available technologies only) the greenhouse warming by 2075 will be between 2°C-6.5°C. I f no action is taken , the warming will be between 3°C-8.5°C.

Five Key Areas

Five major areas for action stand out as essential for controlling the rate and extent of climatic change. These are:

• Controlling those industrial chemicals that affect stratospheric ozone and the radiative balance of the atmosphere;

• Maximizing energy efficiency and the use of renewable energy sources;

• Minimising land-use changes that contribute to climate disruption, for instance through altering the albedo of the earth's surface, or through adding greenhouse gases to the atmosphere;

• Improving the resilience of the biosphere, for example by protecting vegetative cover to enhance C0 2 uptake by photosynthesis;

• Abandoning current concepts of "development", which as presently implemented can only result in environmental and social disruption.

Controlling Industrial Chemicals

Table 1 (page 12) summarises the main trace gases implicated as a cause of climate change. Of these, the halogenated hydrocarbons are only a few decades old. The world, even modern societies, have done without them for years and could dispense with them again. Not all of them are equally potent in affecting

The Ecologist, Vol.19, No.l , 1989 ozone and climate, and the harmless ones could be cleared for use after proper and internationally agreed screening. Collectively the halogenated hydrocarbons are responsible for 80-90 per cent of the ozone problem and 20-30 per cent of the greenhouse problem. Even i f banned today, their impact will continue to be felt at least into the middle of the next century because of their long life spans in the atmosphere (1-3 centuries).54 Nonetheless, they are all man-made and thus (in theory) easy to control. Arrhenius55

has listed the possibilities for reducing the use of the halogenated hydrocarbons(see Table 2). He has urged a complete ban on all halons (brominated halocarbons), on CFC-12, CFC-11, methyl chloroform, CFC-113, CFC-114 and CFC-15.

According to the 1987 Montreal Protocol, emissions in 1993 must be 20 per cent lower than in 1987, and in 1998 50 per cent lower than in 1987. By 2000, atmospheric CFCs will thus still have increased by 50 to 100 per cent. Much sharper targets therefore have to be negotiated.56

Energy Efficiency and Renewable Energy

Few subjects cause more heated discussion than future energy demand and use. Bach57 discusses three possible scenarios. Of these, the 'Oakridge A ' scenario, as developed by Edmonds et al, 5 8 and the 'Efficiency Scenario', developed by Lovins et al.(1981-1983),59 are the most pertinent. 'Oakridge A ' projects a growth in fossil fuel use from 7.83 TW in 1980 to 159 TW by 2100. This would lead to a 22-fold increase in C02 emissions from 1980 to 2100.

strategy, implying that currently available, cost-effective and efficient energy technologies will be introduced over the next fifty years. The scenario adopts a slow reduction rate initially, on the assumption that a rational energy policy will have to overcome many obstructions, and a faster reduction rate later on when the implementation of the myriad possibilities have picked up momentum. The overall reduction rate is 3.2 per cent per year. This leads to a significant reduction of fossil fuel use and the cumulative C02 emission is 1/33 that of the 'Oakridge A ' scenario.

The potentials for maximizing energy efficiency are manifold:

• Only 32 per cent of the energy produced through centralized power generation is used: the rest (some 68 per cent) is wasted as heat. In power/heat co-generation systems, 85 per cent of the energy produced can be used and only 15 per cent wasted. • With automobiles, the average fuel consumption is 10-12 litres/100 km, with the best available car on the market using 5 litres. Yet fuel consumption in the best available prototype is close to 2-3 litres/100 km. • With household electrical appliances, improvements in energy efficiency of up to 50 per cent can be achieved, whilst in heating and cooling systems improvements of up to 80 per cent are possible. In construction materials and buildings, improvements between 30 and 50 per cent could be obtained. Renewable energy sources (such as hydropower, solar energy, wind power, and geothermal power) offer a mixed bag of possibilities.Yet there is every reason to be confident that by 2000 all the renewables together could produce 2 TW, with 5 TW by 2030 and 10 TW.by 2050, depending on the political will to invest in them.

I f we also succeed in greater efficiency of end use, the total world energy demand by the middle of the next century could potentially be covered by renewables only.

Land Use and Greenhouse Gases

A survey of how land use changes contribute to the greenhouse effect has been recently given by Bouwman.61 Changes in vegetation (for example, deforestation) influence reflectivity (albedo), in addition to hydrological cycles (evapotranspiration and precipitation), and, via clouds, the solar radiation balance. Soils under wet conditions, as in marshes and paddy fields, emit methane, and under dry conditions carbon dioxide. Nitrous oxide is emitted from a wide range of soils by microbial transformation of nitrate or ammonia from manure and synthetic fertilizer.

From pre-agricultural time to the present, the distribution of land-cover has changed greatly.62 Carbon released into the atmosphere from forested lands which have been cleared for agriculture makes a major contribution to the greenhouse effect. This transfer is largest in the tropics, but as temperate and boreal forests become increasingly affected by acid rain and by the shift of bioclimatic zones, they will soon become potent contributors. Methane has been found to be rapidly increasing in the atmosphere62 and, per molecule, it is 30 times more potent than C02 as a greenhouse gas.63 Table 3 shows emission rates as a result of various land uses.

Nitric oxide (NO) and nitrogen dioxide do not absorb infrared radiation, but NO plays a role in the destruction of ozone. Nitrous oxide is per molecule about 200 times as potent as C02 in causing